Creating An Antidote For Android Simplelocker Ransomware

In this blog post we'll be creating an antidote for the ransomware to decrypt any files it encrypts.

The process of creating the antidote is actually very simple because the ransomware comes with a built-in decrypt method and cipher password. This means we're able to create our own Java class and copy the decryption code from the ransomware into our antidote class.

So let's jump right in and start creating our antidote for Simplelocker!

We can see that the decrypt() method is clearly provided within this class. We also already know the decryption password (as set in the Constants class), so all we need to is call this method on any files ending in .enc.

Let's create a new Java class called SimplelockerAntidote with a method called getEncryptedFiles() which will scan the current directory for all files ending with .enc:

This method returns an array of String files names (of all files ending in .enc in the current directory) which we can then feed into the decrypt() method. Line 3 sets the current directory (where the Java program is running). Line 10 iterates over all files in the directory. Finally, line 15 checks if the current file ends in .enc where line 17 adds it to the return array if it matches.

Next, create a main method which calls getEncryptedFiles() and sets the decryption password:

It would be fairly straightforward from here to convert this Java program into an Android app. This app could then search for all .enc files on the SD card and attempt to decrypt them - thus providing a direct Android antidote app.

The antidote for this ransomware was incredibly easy to create because the ransomware came with both the decryption method and the decryption password. Therefore producing an antidote was more of a copy-and-paste job than anything.

It's also worth noting that while this antidote doesn't detect the decryption password automatically, it could be possible to do so. However, future versions of the ransomware will probably not reveal the decryption password so easily and will likely receive it from the C&C server.

Since the Simplelocker ransomware is a proof-of-concept, the antidote provided here is simply a solution to this proof-of-concept. Future versions of advanced smartphone ransomware will likely prove significantly harder to reverse engineer.